Electrical transformer and primary winding thereof



I N VEN TOR.

y 1943. c. F. FREY ELECTRICAL TRANSFORMER AND PBIIARY "INDING THEREOF Filed 1m. 5, 1 44 6760/1 flay 77417 m #z mmi 1 z I z z 1 1 I z z 1 z I I z 1 I, 1 4 r I I .2 I

Patented July 13, 1948 ELECTRICAL TRANSFORMER AND PRIMARY WINDING THEREOF Cleon F. Frey, Greenfield, Ind., assignor to P. R.

Mallory & Co., Inc., Indianapolis, Ind., a corporation of Delaware Application December 5, 1944, Serial No. 566,734

'2 Claims. (01. 175-359) The present invention relates to electrical transformers which may be employed for a variety'of purposes, although more particularly designed for advantageous use in an ignition system of the type disclosed in the patent application of Alexander C. Wall for Ignition system and apparatus thereof, Serial No. 549,278, filed August 12, 1944.

A general object 01' the invention is the provision of such an electrical transformer (and the primary winding thereof) which by virtue of a novel construction of the primary winding and resultant structural features of the transformer, though simple and easily constructed and assembled, is exceptionally efiicient, relatively free from capacity loading characteristics and is capable of an unusually long service life.

A more specific object of the invention is to provide such a transformer with telescoped windings of such character and in such fashion that the convolutions of the higher tension end of the primary winding are spaced from the convolutlons of the high tension end of the secondary winding a greater distance than the spacing between the two windings at the low tension ends thereof whereby, when such transformer is used for example in an ignition system for production of fuel charge-igniting sparks of high frequency and voltage at spark plugs, there is an effective minimization of power losses, corona effects and capacity loading with an appreciable and highly desirable avoidance of voltage breakdown tendencies, and which effectively aids in the build-up of desirably high voltages at the spark plug gaps.

A further object of the invention is the provision in such transformer structure of a primary winding which is tapered at its higher tension end easily and effectively to attain desired increased spacing at the high tension end of a substantially cylindrical secondary winding, or the like, when two such windings are telescoped together with their opposed low tension ends arranged opposite each other.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the features of construction, combination of elements and arrangement of parts, which will be exemplified in the construction hereinafter set forth and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in.

connection with the accompanying drawing, in which:

Fig. l is a diagrammatical showing of a portion of an internal combustion engine cylinder and spark plug mounted therein, employed in an ignition system (only part of which is shown) an embodiment of the transformer of the present invention;

Fig. 2 is an enlarged longitudinal sectional view, with parts broken away, of a modified form of transformer of the invention and associated parts of a spark plug employable in such ignition system, etc. and

Fig. 3 is an enlarged longitudinal view, with parts broken away and in section, of a further modification of the primary winding of the present invention which may be employed to advantage in the secondary winding structure and with associated spark plug parts shown by way of ex ample in Fig, 2. v

In the above identified Alexander C. Wall application it has been proposed to provide a certain specific ignition system for internal combustion engines which generates electrical energy of relatively low frequency and voltage, distributes that energy toward the spark plugs of the various cylinders, then converts the energy to a high' frequency current and finally transforms the relatively low voltage high frequency energy to high frequency energy at relatively high voltage for supply to the spark plug gaps. That specific system has proven to be highly effective in minimizing power losses to produce strong effective sparks at the spark plug gaps and very satisfactory for use with aircraft engines where conditions due to extreme and rapid changes in altitude and the dictates of that particular service normally tend to cause a variety of ignition troubles; and particularly in view of the eiiicacy thereof in overcoming the normally serious problems of radio interference. It has been found in accordance with the present invention that the performance of such system may be further enhanced by the employment therein of transformer apparatus of the present invention, embodiments of which are shown in the drawing, in which like numerals identify like parts throughout.

In Fig. 1 is diagrammatically shown a portion of a typical circuit of such an ignition system. A portion ill of a cylinder wall is fitted in the usual manner with a spark plug structure ll comprising a shell or metallic casing l2, one or more spark plug electrodes l3l3 carried by easing l2 and a central spark plug electrode l4.

The spark plug shell or casing l2 houses a transformer ii of the present invention.

This transformer structure I5 may include an elongated substantially cylindrical secondary winding l6, preferably wound about the exterior of a substantially cylindrical elongated cup or vial ll of suitable insulating material, preferably glass, of a minimum wall thickness for separation of a primary winding [8 from the secondary winding H5 at a minimum distance. The thin vial ll preferably is made from heat-resistant glass having a low coeificient of expansion but other glass materials such as lead glass may be employed provided thin layers thereof are of such character as to withstand the high temperatures and voltages to which they are subjected in operation of the system, in which voltage stresses of the order of 2,000 to 3,000 volts per mil may be common and localized stresses may at times be as high as about 10,000 volts per mil.

The secondary winding I6 is arranged upon the glass cup I! with the low tension end at l9 located adjacent the rim of the cup and the high tension end at 20 located adjacent the closed end or relatively flat bottom of the cup. Preferably the low tension end of the secondary winding I8 is anchored at 19 directly to the surface of the glass cup I! by a body or smear of metallic material, such as a silver compound which may be adhered to the glass by firing, preferably tinned with solder to anchor the wire, and which may also be employed for anchorage of means 2| for grounding the low tension end of the secondary winding iii to the spark plug shell [2. The high tension end of the winding I6 is preferably anchored in a similar manner to the relatively flat bottom of the cup I! by means of another smear or body 22 of similar metallic material which, with or without-other associate means, may be employed to provide for connecting contact with a head 23 of central electrode M.

The primary winding I8 is, as shown, telescoped with the secondary winding l6, such as by being received or socketed within the glass cup 11. Its low tension end at 24 is connected to a return conductor 25 in turn preferably grounded, such as by connection at any suitable point as at 26 to a grounded shielding cable sheath 21. The relatively higher or medium tension end of the primary winding l8, at 28 opposite the high tension end 20 of the secondary winding i6, is connected to a supply conductor 29 to which is fed relatively low tension high frequency energy from any suitable source of supply not shown.

It will be noted in Fig. 1 that, in accordance with the present invention, the convolutions of the primary winding l8 at its higher tension end 23 are spaced farther from the convolutions of the secondary winding at its higher tension end at 20 than are the convolutions of the primary winding at its low tension end at 24 spaced from the convolutions of the secondary winding at its low tension end at i9. This may be attained by tapering the primary winding ill at its higher tension end at 28, such as by making convolutions thereof of successively decreasing diameter.

As shown in the embodiment depicted in Fig. 2, the transformer secondary assembly including the vial i1 and the secondary winding l6 may be removably mounted in a chamber 30 of a conventional spark plug structure which may comprise a metallic casing or shell l2 lined with a sleeve .3I of suitable insulating material, such as a heat-stable ceramic or porcelain, and in which is suitably supported the central electrode i4 with its terminal button or head 23 exposed in the bottom of chamber 30. The metallic casing or shell I2 is provided with external threads 32 for demountable mounting thereto of anchoring means for a connecting cable, such as a sleeve nut 33.

With the secondary assembly seated in chamber 30 electrical connection between the terminal of the high tension end 20 comprising the silver solder smear 22 and the electrode button 23 may be accomplished by any suitable means, such as by a tapered helical spring 34 which may also provide a desired resilient mechanical support. The low tension end at l9 may be grounded to the casing 12 by means of a pigtail 2| clamped between an edge or inturned end flange 35 of easing l2 and cable-end structure by means of the anchoring sleeve nut 33. However, ii desired, the transformer secondary assembly may be permanently mounted within the chamber 30 by a soldered connection at 2| between the terminal for the low tension end at l9 and the edge 35 of the casing l2, or by a body of solder bridging across between the spark plug casing or shell l2 and the anchorage smear at l9, or by any other suitable anchoring means that may readily occur to one skilled in the art.

The primary winding I8 is supported and constructed in a manner to be received or socketed in the glass cup 11 with convolutions of that winding at the low tension end 24 spaced by the glass cup from convolutions of the secondary winding 16 at a minimum distance to assure the attainment of eflicient coupling. This primary winding construction may, as shown in Fig. 2, comprise a core of suitable heat-stable insulating material, preferably in 'the form of an elongated tapered or conical body 36 having a base portion 31, an intermediate flange 38 providing a shoulder 39, and an end centering flange 40. A helical groove 4| is provided on the tapered portion 38, in which the wire of the primary winding I8 is received and seated. The core 38-40 may be formed from any insulating materials which will withstand the high temperatures encountered at the spark plugs without giving off gases, which would tend to cause gas-filled voids within the transformer giving rise to corona effects during engine operation; such as inorganic materials, e. g., glass or a material formed of compressed mica particles and an inert filler or other materials such as heat-stable plastics or a thermosettlng phenolic resin if subjected to a sufllcient prebaking period, e. g., about twenty-four hours at about C. The core 3640 is provided with an axial bore 42 which near the end flange 40 communicates with the groove 4i by means of a hole 43 through which the higher tension end 28 of the primary winding l8 makes connection with the supply cable conductor 29 located in the axial bore. The low tension end 24 of the primary winding I! may be threaded up through a longitudinally extending hole 44 in the base portion 31 of the core to serve as a terminal for connection to the circuit cable conductor 25.

With the primary assembly socketed into the glass cup I! for magnetic coupling of convolutions of the primary winding I8 with convolutions of the secondary winding [6, this transformer structure preferably is thoroughly saturated or impregnated with a suitable insulating compound to eliminate all gasor air-filled voids toavoid corona effect and attendant energy loss, Relatively high operating temperatures at the transformer spark plug unit must be taken into account and only such insulating compounds-as will effectively stand up under the rigid operating conditions should be employed. The entire transformer spark plug unit should be thoroughly saturated and impregnated with a suitable insulating compound such as a fluid polymering resin which will be transformed by heat into a. heatstable solid or semi-solid. Such material, if desired, may be filled with particles of refractory material such as ground glass, asbestos, mica, or

the like. If the mechanical structure is such as to assure hermetic sealing of the parts within the encasing shell, a heat-stable non-polymerizing fluid may be employed. It has been found that various insulating fluids known in the industry are satisfactory for this purpose. A body of such impregnating compound is indicated at The primary assembly is held in assembled position socketed within the vial l1 and telescoped with the secondary winding IS with both windings located within the chamber 30 in the spark plug shell or casing 12, preferably by means of the internally threaded sleeve nut 33 threadably engaged with'the external threads 32. The sleeve nut 33 preferably has a flange 4B engaged behind a flange 41 on a metallic sleeve or ferrule the convolutions of the primary winding and the convolutions of the secondary winding at the low tension ends thereof assures efllclent attainment and maintenance of the necessary coupling. The increased spacing atthe higher tension ends such as by virtue of the tapering of the primary winding effectively minimizes capacity to avoidundesirable capacity loading. Further the increased spacing at the portions of the windings where potential difference is great tends to avoid voltage breakdown and reduces power losses and any tendencies to corona effect. This feature also helps build up the voltage at the spark plug 1 during sparking at the spark plug gaps when fre- 48, positioned about the core base portion 31, with an internal shoulder in the sleeve 48 bearing against the core shoulder 39, as shown in Fig. 2. The outward and of the sleeve 48 is thus forced toward the end edge of the spark plug shell or casing l2 by the sleeve nut 33 when it is tightened up to clamp, if desired, the secondary terminal or pigtail 2| between shell end edge 35 and the core flange 38 and/or the end of the sleeve 00 to ground the low tension end it of the secondary winding i6 and to make good electrical connection between the spark plug casing or shell and the sleeve 48. Preferably the shielding sheath 21 is provided for the supply conductors 25 and 19, which may comprise a continuous metallic hose of bellows construction and an overlying protective bronze braid suitably anchored to the anchoring sleeve 08 such as by solder.

The transformer assembly of a typical embodiment of the invention for employment in such an ignition system is in overall dimensions about one inch long and about three-eighths of an inch in diameter, and has a turn-ratio of the order of 15 to 20:1 with the secondary winding having about 400 turns of fine wire, such as No. 40 or 42.

It has. been found in the operation of such an ignition system that the electrical power supply unit, such as a standard magneto, may deliver current of approximately 1,000 cycles at a peak voltage of about 1,000 to 1,500 volts through thedistributor at proper timing successively to the various supply circuits, each of which may include a condenser, a spark gap and the transformer primary-winding i8 connected in series to provide an oscillatory circuit in which, with a total impulse energy of about '7 millijoules, a high frequency current at, say, 1,000 volts peak and approximately 1 to 2 megacycles will be caused to flow. With the employment of a transformer of the invention having a turn-ratio of the order of 15 to 20:1 and a secondary winding of about 400 turns, the peak voltage of the relatively high frequency energy can be stepped up to in excess of 20,000 volts, possibly about 40,000 volts. As a result high frequency sparks are created at the gaps between the spark plug electrodes ill and l3-l3, which efficiently fire charges of fuel even though the spark plug electrodes be fouled with carbon and/or oil. The close spacing between quencies of the order of 200 megacycles are present, there is an appreciable non-uniformity of distribution of stress which concentrates the potential difference at the higher tension ends, 1. e., at the bottom of the primary winding-receiving vial. Thus tapering about a third of the primary winding at its higher tension end appears to relieve the stresses sumciently for all practical purposes, although a slightly better performance may be attained by a complete tapering of the primary winding.

Such a proposal is made in Fig. 3 wherein is shown a primary winding having only about a tthird thereof at its-higher tension end tapered.

That structure, by way of example, comprises a cylindrical collar 5i of metallic material provided with a laterally extending flange 52. A body 53 of suitable insulating material, such as glass preferably fused to the collar 5|, supports and properly centers an axial conductor 54, an exposed end 55 of which is adapted to be connected to or to make contact with a supply conductor such as 20 shown in Fig. 1. Preferably the collar 5i is of such diameter as to be rather snugly received in the open mouth of the vial I1 and thus it is indented at 56 there to receive the end 89 of the winding I8, which is suitably anchored in position such as by solder. The higher tension end of the winding at 28 is anchored to the conductor 54 in any suitable manner, such as by solder.

It will be noted from Fig. 3 that the convolutions of winding it from the low tension end at it to a point at 51 about two thirds the axial distance from l9 are of substantially equal diameter, but that therebeyond they are of successively decreasing diameter, which in tests of models of that structure such tapering has been found to be effective in the attainment of the results desired.

It is to be understood that to employ the primary assembly of Fig. 3 it may be placed or socketed in vial l1 so that winding [8 is telescoped with the secondary winding I6 on the vial. The flange 52 is to serve as the connector 2], such as by being clamped between end flange 35 of the spark plug shell l2 and ceramic sleeve 32, or by being anchored thereto by any suitable means such as by soldering, or clamped thereto by cable and structure when drawn up by sleeve nut 33;

with a terminal end of supply conductor. pulled into secure contact with the end 55 of axial conductor 54, all as may be easily understood from an inspection of Fig. 11 of the above identi fied Alexander 0; Wall patent application. course, it isto be understood that in such case the body 45 of insulating compound fills all voids within the vial H, including the interior of the primary winding i8. 7 1

It will thus be seen that the objectsset forth above are efficiently attained by the present in-' vention'and since certain changes may be made in the above construction and different embodiments of the invention could be made without departing from th scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative'and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described,

and all statements of the scope of the invention which, as a matter of language might be said to fall therebetween. I

Having described my invention, what I claim as new and desire'fto secure by Letters Patent is:

1. A transformer adapted toflt into the barrel of a spark plug which comprises a cup shaped coil form of insulative materiaL'the walls of the cup defining a cylindrical coil form of slightly less diameter than the inner surface of the spark plug barrel, a secondary winding on the outer surface of said coil form comprisinga single row of turns of substantially uniform diameter, a plug havinga cylindrical end portion fitting snugly against the inner surface of the coil form and a flange for engaging the rim of the cup shaped coil form whereby the plug is reniovably socketed in the cup, and a primary winding supported by said plug and extending into said coil form, said primary winding comprising a single row of turns,

the part of the primary winding adjacent the high tension. end of the secondary Winding being file of this patent:

or reduced diameter as compared to th part of the primary winding adjacent the lowtension end of the secondary winding.

2. A transformer adapted to fit into the barrel or a spark plug which comprises a hollow cylindrical coil form of insulative material which is of slightly less diameter than the spark plug barrel, a secondary winding wound on the outer su face of said coil form comprising a single row of turns of substantially uniform diameter, a plug having spaced cylindrical end portions fitting snugly against the inner surface of said coil form whereby the plug is removably socketed within said coil form, said plu having a tapered portion intermediate said cylindrical end portions, and a primary winding comprising a. single row of turns wound on the tapered portion of said plug so that the part of the primary winding adjacent the high tension end of the secondary winding is of reduced diameter as compared to the v The following references are of record in the UNITED STATES PATENTS Number Name Date 1,011,884 Cavanagh Dec. 12, 1911 1,713,214 Brand May 14, 1929 1,739,818 Beals Dec. 17, 1929 1,898,931 Bahrmann Feb. 21, 1933 1,940,840 Bellaschi Dec, 26, 1933 1,984,979 Molter Dec. 18, 1934 2,153,090 Libbe Apr, 4, 1939 2,255,730 Frazier. Sept. 9, 1941 2,414,692 Harkness et a1 Jan. 21, 1947 FOREIGN PATENTS Number Country Date 344,181 Great Britain Mar. 5, 1931 532,717

France Feb. 10, 1922 

